Joists or structural beams of the T-type (as used herein the term T-type shall also include twin T and quad T-types) are well known in the art. The ledge or ledges of this type of joists contain the main reinforcing of the structural member and act as the supporting member from which the ceiling is suspended. In the past, various expedients have been used to attach the wall or ceiling board to the ends of the ledges of the joists. The most common expedient is the use of the so-called "nailing strips" incorporated into the ends of the ledges. The nailing strips are ordinarily mechanically attached to the outside of a ledge as exemplified by the structure shown in U.S. Pat. No. 2,123,923. They are adapted to receive bolts, screws, nails and the like to secure the wall board or other structural element to the ledges. The nails or screws are driven or screwed into a wooden beam, disposed behind the plate, after passing through the nailing plate itself.
Various means have been used to affix the nailing plate to the end of the ledges as shown in the above-referenced patent and in U.S. Pat. No. 1,466,264, for example. Anchors for supporting structural elements on the end of the ledges have been incorporated into the ends of the ledges by various means as illustrated by U.S. Pat. Nos. 1,251,150 and 1,953,138. Other patents relating generally to the field of this invention are U.S. Pat. No. 1,470,727 and British Pat. No. 838,452.
The known expedients for attaching nailing plates to the ends of the ledges of T-type joists are subject to various disadvantages. Wooden nailing plates are subject to shrinkage, rotting, destruction by termites and the like so that they are not generally satisfactory for permanent installations. The metal anchors, hooks and the like are subject to the disadvantage, along with the wooden nailing plates, that their installation is difficult and time-consuming and, consequently, expensive.
Heretofore, various structural elements have been proposed which have a fire rating of approximately two hours when tested with the standard time-temperature curve established by the American Standards for Testing Materials. However, any such structural element incorporating therein a T-type joist and which has successfully met this requirement involves the use of a T-type joist requiring approximately twice as much concrete to form as required in the structural element of this invention. More concrete was required to form the prior art type of joist since either thicker plate-like body portions and/or more massive ledges were required in order to withstand the temperatures involved.
Accordingly, it is a principal object of this invention to provide a novel structural element having a fire rating of approximately two hours when tested with the standard time-temperature curve established by the American Standards for Testing Materials, particularly when tested under the unrestrained assembly classification.
Another object of this invention is to provide a structural element as aforesaid comprising one or more prestressed concrete joists, each joist having a plate-like body portion forming at least a part of a first side of said element one or more integrally formed, reinforced support ledges disposed normal to the plate-like body portion, and a nailing strip integrally molded in the bottom of each ledge, each nailing strip including a penetratable area formed internally adjacent thereof, a plurality of sheets of material disposed adjacent the ends of said ledges, each sheet being formed from a material from the class consisting of gypsum or a mineral fiber mixture, said sheets forming the second side of said element and having a thickness equalling one-half inch or more, each sheet of material forming at least one butt joint with an adjacent sheet wherein said butt joint extends longitudinally along a portion of one of said ledges, a plurality of channel-shaped members disposed along each butt joint and intermediate said ledge portion and said sheets, attachment means for attaching said channel-shaped member to the nailing strips of said ledge portions, and additional attachment means for attaching said sheets of material to said nailing strips and said channel-shaped members, said additional attachment means, channel-shaped members and nailing strips cooperating to secure the sheets of said joist while preventing undesirable distortion or warping thereof during the fire rating test.
Another object of this invention is to provide a structural element as aforesaid in which each of the additional attachment means used to attach the sheets of material to the channel-shaped members disposed along said butt joints is positioned a minimum distance of approximately one and one-fourth inches from the adjacent edge of each sheet.
Another object of this invention is to provide a structural element as aforedescribed in which each ledge of each joist has a plate-like body portion associated therewith, each ledge being disposed generally centrally of said associated part, each associated part extending laterally of both sides of its associated ledge, taken along a line disposed normal to the longitudinal axis of its associated ledge to a point midway between said associated ledge and an adjacent ledge or the end of said plate-like body portion, whichever is the closer, the ratio of the cross-sectional area of the part of said plate-like body portion taken along a line disposed normal to the longitudinal axis of said ledge, to the width of its associated ledge, said width of said ledge being measured along a line normal to the longitudinal axis of said associated ledge at the line of intersection of said ledge with said part, varying between approximately 7.5 to 10 inches, and the ratio of the cross-sectional area of each ledge to the cross-sectional area of its associated part, taken along a line disposed normal to the longitudinal axis of said ledge, being equal to approximately 2 or less.
Another object of this invention is to provide a structural element as aforesaid in which the ratio of the cross-sectional area of the part of the plate-like body portion to the width of its associated ledge varies between approximately 8 to 9 inches and the ratio of the cross-sectional area of each ledge to each cross-sectional area of its associated part is equal to approximately one or less.
Another object of this invention is to provide a pretensioned concrete joist of the T-type comprising a concrete plate-like body portion, a channel-shaped concrete support ledge disposed normal to said body portion along the length thereof, a nailing strip integrally molded in the bottom of said ledge, said nailing strip comprising a channel-shaped member, a longitudinally extending U-shaped portion formed along the upper edge of each side wall of each channel-shaped member with the longitudinal axis of each U-shaped portion lying in a plane in which is disposed generally parallel with the plane in which is disposed the bottom wall of said channel-shaped member and the bight of each U-shaped portion extending inwardly of its associated side wall, and a longitudinally extending penetratable layer of material disposed within said channel-shaped member, said layer of material having a lower surface portion disposed in contact with the bottom wall of said channel-shaped member and upper surface portions disposed in abutting contact with said U-shaped portions of said channel-shaped member, said nailing strip also including a plurality of positioning members longitudinally spaced along said channel-shaped member and having portions thereof disposed within the U-shaped portions extending longitudinally along the upper edge of each side wall of said channel-shaped member, and pretensioning steel extending longitudinally of said ledge and disposed in contacting engagement with the upper surface of said positioning members, said pretensioning steel and said positioning members cooperating to secure and maintain the nailing strip on the bottom surface of the ledge prior to and during placing of the concrete during forming of the joist.
Another object of this invention is to provide a pretensioned concrete joist as aforedescribed in which each of said positioning members comprises an elongate support portion, and a pair of L-shaped portions each L-shaped portion including a pair of arms, each L-shaped portion depending from a corresponding one of the arms of said support portions and having one of said arms disposed parallel with said support portion, each L-shaped portion being constructed for limited pivotal movement relative to said support portion, each free end of the arms that are disposed generally parallel with said support portion being positioned within a corresponding one of the longitudinally extending U-shaped portions formed along the upper edge of each side wall of said channel-shaped member.
Another object of this invention is to provide a form member for use with a mold for making a pretensioned concrete member having a nailing strip molded therein, said form member comprising a longitudinally extending, channel-shaped member for disposition in the bottom of said mold member and a plurality of positioning members longitudinally spaced along said channel-shaped member and secured thereto.
Another object of this invention is to provide a novel positioning member for positioning an object in a hollow member such as a mold member, said positioning member being formed from a single piece of plastic material and comprising an elongate support portion the upper surface of which is concave in configuration, and a pair of L-shaped portions, each L-shaped portion including a pair of arms, each L-shaped portion depending from a corresponding one of the ends of said support portions and having one of said arms disposed parallel with said support portion, each L-shaped portion being constructed for limited pivotal movement relative to said support portion, and the free ends of said arms that are disposed generally parallel with said support portion, lying generally in a common plane and spaced apart one from the other, said free ends being constructed for engaging a portion of the object.
Another object of this invention is to provide a novel positioning member as aforesaid in which each of the arms of said L-shaped portions that are integrally attached to said support portion are convergently disposed one to the other in a direction proceeding from said support portion toward the arms disposed generally parallel with said support portion.
Another object of this invention is to provide a novel positioning member as aforedescribed in which the angle of convergence of the arms that are integrally attached to said support portion equals at least approximately 4.degree. or more, and preferably approximately 6.degree..
Another object of this invention is to provide a novel positioning member as aforedescribed in which the upper surface of said support portion is concave in configuration.
Another object of this invention is to provide a novel positioning member as aforedescribed including means interconnecting a portion adjacent the free end of each arm disposed generally parallel with said support portion thereby preventing undesirable entanglement of one plastic member with another when packed "loosely" in a container.
Another object of this invention is to provide a novel positioning member including tab means extending longitudinally outwardly of the opposite ends of said support portion and longitudinally outwardly of the pair of arms disposed generally parallel with said support portion.
Another object of this invention is to provide a novel positioning member as aforedescribed in which each free end of each arm lying generally in a common plane includes a portion disposed generally normal to the longitudinal axis of its corresponding arm and likewise is disposed within said common plane.
Another object of this invention is to provide a novel positioning member as aforedescribed in which each L-sahped portion includes stiffening means for controlling the overall stiffness thereof wherein said stiffening means preferably includes a diagonally disposed member interconnecting the arms of each L-shaped portion.
Another object of this invention is to provide a novel positioning member as aforedescribed in which the outer ends of said support portion and said L-shaped portions are connected by a pair of convergently disposed lines proceeding along said lines in a direction from each outer end of said support portion to the corresponding outer end of said L-shaped portion.